1. Field of the Invention
The present invention relates to a process for melting a charge in a furnace, in particular an electrical arc furnace, by supplying energy of fusion to the charge, in which gases, and notably at least one combustible gas, in particular carbon monoxide, are generated during the melting of the charge, in which process an oxidant gas containing more than 25% by volume of oxygen is injected during at least some periods, in order to carry out post-combustion of the combustible gases.
The term "oxidant gas containing more than 25% by volume of oxygen" means a gas which contains at least 25% by volume of oxygen under standard temperature and pressure conditions, in particular oxygen-enriched air containing preferably more than 50% by volume of oxygen, but more preferably oxygen which is industrially pure, that is to say having at least 88% by volume of oxygen, including in particular oxygen generated by adsorption equipment of the VSA (Vacuum Switch Adsorption) type, or any other generator of industrially pure oxygen, including systems employing membranes.
2. Description of the Related Art
In an electrical arc furnace, in particular an electrical arc furnace for melting scrap with a view to the production of steels, the scrap is melted essentially by supplying energy of fusion to this charge through graphite electrodes of the furnace, through which a very heavy current is passed so as to release a sufficient amount of energy to melt the scrap present in the said furnace.
Fossil energy is currently being used more and more to increase the productivity of these furnaces. Hence, the use of coals charged in baskets or injected through lances permits the use ossil energy. This energy is only partially used insofar as the combustion of the coal is incomplete. Thus, large quantities of carbon monoxide, CO, are themselves released by the oxidation of the carbon. This carbon monoxide is burnt with oxygen in the furnace according to the process termed post-combustion for an electrical arc furnace and described, for example, in U.S. Pat. Nos. 5,166,950, 5,373,530 and EP-A-127,492.
U.S. Pat. No. 5,166,950, in the name of the Applicant Company, describes a process and an installation for melting a charge in, notably, an electrical arc furnace for melting scrap and producing steels, by supplying energy of fusion to the charge and with post-combustion of the fumes by injecting an oxygen-containing gas into a space of the furnace located above the charge. In the process described, the oxygen injectors are used to create rotating gas streams turning in opposite directions in the space of the furnace located above the charge. The effect of this is to ensure effective mixing of the oxygen-containing oxidant gas with the combustible gases present, such as the carbon monoxide and/or hydrogen produced by the charge, so as to cause uniform post-combustion of these gases in the furnace, which post-combustion contributes to the melting of this charge in cooperation with the vertical electrodes distributed around and in the vicinity of the vertical axis of the furnace.
U.S. Pat. No. 5,373,530 (as well as EP-A-127,492) describe an oxygen-containing gas injector passing through the casing of the furnace in order to deliver an oxygen-containing gas jet which is non-radial with respect to the axis of the furnace.
A post-combustion process for an electrical arc furnace is also known from the article "Oxygen Injection for Effective Post-Combustion in the Electrical Arc Furnace", P. Mathur and G. Daughtridge, this process using oxygen injection above the pool at a supersonic speed (in general greater than 300 m/s), in which the oxygen strikes the surface of the molten metal pool (the slag), which causes oxidation of the iron in form of iron oxide FeO, oxidation of the iron with the carbon dioxide gas which is present, generating iron oxide FeO, carbon monoxide, as well as a reaction of the carbon with the carbon dioxide to generate carbon monoxide. This supersonic oxygen injection thus generates a gas mixture containing a quantity of carbon dioxide gas and also a quantity of carbon monoxide, which results notably from the aforementioned reactions. Thus, the drawback of such a process is that it does not fully use the possibility of generating energy by employing the carbon monoxide produced in the furnace.